Primum Non Nocere
by TotallyUtterlySherlocked
Summary: "First do no harm." That had been the basis for an entire lesson in John's university bioethics class. It was something he'd always remembered. He kept it in mind, always, on the battlefield, and in his own locum work. Now, when he's living out his own medical nightmare, he must force Sherlock to break one of the principles of medicine he'd spent his entire life protecting.
1. An Episode of Syncope

**A/N: I'm the worst person in existence, OK? I'm just establishing that immediately so there are no questions about my motives by the end of this story.**

**DISCLAIMER: I own nothing. Please don't sue me.**

* * *

It was an ordinary day on Baker Street, and even more ordinary inside 221B.

Of course, in 221B, _ordinary_ was a very relative term.

Ordinary in this case meant John waking up with a start due to a deafening bang from the kitchen downstairs. He glanced at the clock and groaned. It was 5 AM. It was his day off. And the bloody headache he'd had when he went to bed hadn't gone away.

When he'd managed to push himself out of bed and down the stairs, the pounding behind his eyes was enough to make him wince. He made a conscious effort to maintain a neutral, if slightly annoyed, expression when he'd gotten to the kitchen, where Sherlock seemed to be deep in an experiment involving...kidneys, and something that looked highly acidic.

"What was that bang?" He asked, now unsure if he really _wanted_ to know.

"Hmm?" Sherlock didn't even bother to look at him.

"I said," John stopped, gritted his teeth against a wave of pain, and then continued. "What was that bang?"

The detective looked up, studied John, then looked down. "You ought to get those headaches checked out," he said distractedly.

"Sherlock," John's tone was bordering on edgy.

Huffing, Sherlock stared at him. "I might've lit a tea bag on fire and attempted to extinguish it with acid." He said, clearly annoyed at having to explain himself.

Ordinarily John would've been furious, but honestly, he was in too much pain, too exhausted, and...too...dizzy?

He opened his mouth to say something else, probably to tell Sherlock he was going to faint, but he was unconscious before he could get a word out.

* * *

He woke slowly, and it took him a few minutes to work out exactly where he was. _Hospital_, his mind told him. The bright light was nearly blinding when he opened his eyes, and he blinked quickly to rid his vision of the colored flashes. He saw Sherlock in a hard plastic visitor's chair next to his bed, fingers flying across the screen of his mobile.

John opened his mouth to ask what the hell had happened, and Sherlock answered before he'd said anything. "You fainted," He looked at John and pocketed his phone in one fluid motion.

"And this necessitated a trip to hospital...why, exactly?" John arched an eyebrow.

Rolling his eyes, Sherlock breathed a heavy sigh through his nose. "Because," he began, already losing his final (thin) shreds of patience. "I couldn't get you to wake up. Nor could Mrs. Hudson, and she was really the impetus behind this," He gestured vaguely around the room. "I was content to let you regain consciousness on your own; your pupils were equal and reactive and you hadn't hit your head on anything hard enough to suggest any sort of brain injury."

John blinked at him stupidly. "Have you been reading my medical textbooks again?"

"No," snapped the detective. "I_'_m not _stupid_, John. I delete things that are unnecessary to my work, and any of those facts could prove vital in establishing a cause of death."

Slowly, John nodded. "Yeah," he said in a distant sounding voice. "You're not stupid at all. That's exactly why you _set a tea bag on fire and tried to extinguish it with acid_." He screwed his eyes up and fixed Sherlock with a glare. Sherlock, to his credit, did his best to look uncomfortable, then broke eye contact.

He was spared one of John's famous lectures by the timely arrival of the on-call doctor. Who looked as though he'd just been plucked from a secondary school graduation ceremony.

Immediately he looked at the chart he held in one hand. "Mr. Watson?" He smiled charismatically, and Sherlock rolled his eyes. "Doctor," he mumbled.

The young man looked at him, confused. "Pardon?"

Huffing a sigh, Sherlock fixed the young doctor with a very patronizing sort of look. "He is Dr. Watson. Not Mr. Watson." He pulled out his mobile and turned away in the chair.

Frowning, John looked apologetically at the red-haired doctor. "Sorry about him," he said kindly.

The man smiled. "No, my apologies Dr. Watson. I'm Dr. Kent. Now," He flipped to another page of John's chart. "Your vitals all look stable, but we did an MRI, CT scan, and a head x-ray when you were brought in just in case. Once those come back, and they look clear, you can go ahead and go home."

John grinned. He _loathed_ hospitals, despite working as a doctor. He'd spent far too much time in them before he came back to England. "Please," he said, extending a hand. "Call me John."

* * *

**A/N: I hope you all enjoy this story; as horribly as it's going to hurt me I'm excited to write it!**

**Please review and...**

**DFTBA darlings, :)**


	2. Grade Three

**A/N: Well. It's been a while, hasn't it? No excuses here, just an apology and a chapter.**

**DISCLAIMER: I own nothing, and I am not a doctor, just a mortal muddling through with the help of Google. Please don't sue me.**

* * *

As soon as Dr. Kent walked in, John knew it wasn't good news.

"You found something," he said flatly.

The other man looked apologetic. "John, I'm sorry." He looked down at the radiograph in his hand. "When I was reviewing your CT scan, we saw a mass. It might be nothing-"

"Or it could be cancer." John interrupted, crossing his arms.

"Exactly." Dr. Kent nodded. "I hate to ask this of you but, I need your permission for a biopsy."

John closed his eyes and scrubbed his hands down his face. "Fine," he said, voice muffled by one palm. "You have my permission."

Dr. Kent smiled a little. "Thank you, John. We won't be doing anything until tomorrow morning so we're going to move you upstairs to Neuro just in case. Should I, ah-"

"No need," Sherlock interrupted, striding into John's little room. The blonde rolled his eyes.

"Fantastic." He muttered.

* * *

"They suspect _cancer_?" Sherlock looked...dumbstruck. The expression looked so unnatural on the detective that ordinarily, John would have laughed his arse off. Since he was still battling this bloody headache, he only quirked a smile.

"Not quite," he assured. "But apparently they did find a mass in my CT scan. Better safe than sorry."

Sherlock stared for a minute. "It could be benign," he said, sounding almost as if he was asking for reassurance.

John nodded.

In the next second, Sherlock frowned. "Or it could be malignant." His voice was flat.

Sighing, John nodded again. "We'll cross that bridge when we come to it, Sherlock. For now, I'm just hoping someone can give me something to stop this God-awful headache."

At that moment, a friendly looking orderly stepped into John's cubicle. "Hello Dr. Watson!" Her voice was cheerful, and she smiled broadly at them, not faltering when Sherlock glared at her. "I'm here to bring you upstairs,"

John studiously ignored Sherlock's mumbled "Obvious". "Great," he said, returning the woman's smile.

* * *

That night brought little sleep for John. He'd managed a bit after his nurse dosed him with hydrocodone, but now the anxiety over his biopsy left him staring numbly at the ceiling.

Far too soon, sunlight was peeking in through the slats of the blinds. John did his best to ignore the growing pit of anxiety gnawing at his gut. He sighed heavily, then yelped when he looked to the door and found Sherlock. "Jesus Christ, Sherlock," he panted.

Sherlock just quirked a brow at him. "You're less observant than usual," was all he said.

"I'm a bit distracted you arse," John sniped back, immediately regretting his words when Sherlock looked wounded.

"Sorry," he muttered, reddening a little. "I'm just...God, Sherlock, this is terrifying." Sherlock didn't say anything, just stared. That unnerved John a little, but he pressed on. "I mean, my mum had cancer when I was in uni but she ended up okay. I'm not exactly the most optimistic person but I guess I'm hoping that if she beat it, I could too." He exhaled sharply.

"John," Sherlock's voice was quiet, softened a little around the edges. "I promise you, no matter what ends up happening after today, you are not dealing with this alone. I will be present for any appointments needed, and if need be," Here he paused to inhale deeply through his nose. "I will call on _Mycroft_." Sherlock spat out his brother's name like it tasted bad.

This brightened John a little, and he smiled. "Thank you, Sherlock. Really." The detective nodded solemnly.

At that moment, there was a sharp knock at the open door. John licked nervously at his dry lips. A burly male nurse stepped into the room, glancing swiftly and unsmiling between John and the clipboard he held. "John Watson?" The doctor nodded, lips pressed tightly together.

"I'll see you in recovery," said Sherlock swiftly, giving John's shoulder a quick, awkward squeeze.

John swallowed hard. "Yep," he replied hoarsely.

* * *

Hours later find John blinking slowly awake, briefly forgetting where he was and why he was there. After a few minutes of confusion, his head cleared and he felt his stomach cramp with anxiety. "Sherlock?" He sounded hesitant.

"I'm right here, John," The voice came from John's left, and when he looked over he almost sagged with relief. The detective had contorted himself into one of the hard plastic visitors' chairs. John smiled tiredly at him. He gestured up towards his own head. "How bad does it look?"

Sherlock studied him for a moment before flapping a hand at him dismissively. "Hardly noticeable," he assured John, smiling a bit in return.

There was a rustling as the curtain to John's bed was pulled aside, revealing a grim looking Dr. Kent. John's stomach dropped like a stone. "It's cancer," His voice was remarkably steady.

The other doctor sighed heavily. "It is," he confirmed, looking between John and Sherlock before consulting his clipboard. "Ependymoma to be specific."

"Shit!" John snapped. "What type?"

Dr. Kent swallowed visibly. "Anaplastic. Grade three. We did remove the whole thing during the biopsy," he offered lamely.

"What are my options?" demanded John.

"Radiation is the best option," replied Dr. Kent.

John let out a shaky breath, closing his eyes and clenching his fists. When he opened them, he looked at Sherlock, who was entirely motionless. "Sherlock?" he tried.

Without a word, Sherlock fled, sparing neither man a glance.

Dr. Kent sighed. "So, radiation?" he asked finally.

John bit his lip hard enough to taste blood. "Yeah. I guess so."

* * *

**A/N: This is just another reminder that I am definitely not a doctor. Not an oncologist, not a neurologist, nothing. If any medical experts are reading this and have corrections or advice, I'd love them! Honestly.**

**Thank you so much for reading. Please review and...**

**DFTBA darlings, :)**


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